1. Field of the Invention
This invention relates to electromagnetic apparatus for use in electrical induction devices such as inductors, transformers, motors, generators and the like.
2. Description of the Prior Art
In the manufacture of shell-type transformers, the primary and secondary windings are formed into a common ring having a central opening or window. Two or more rings of magnetic core material are cut open, threaded through the winding window and closed, so that the rings of core material are distributed about the periphery of and encircle the windings. One of the problems with shell-type transformers is the difficulty of cutting and shaping the core material without degrading its magnetic properties. To overcome this problem, coretype transformers have been proposed wherein the core is formed into a ring, which is encircled by two or more groups of primary and secondary windings distributed around the periphery of the ring. Such core-type transformers are bulky and inefficient in terms of material utilization. Moreover, in transformers of the types described above, heat developed by the windings and core during operation oftentimes results in a temperature rise of more than 50.degree. C., increasing the deterioration rate of solid insulating materials in the core and windings as well as the liquid coolant in which the transformer is immersed. For these reasons, transformers of the type described generally result in higher purchase and maintenance costs and lower operating efficiencies than are considered desirable.